I encountered a problem while trying to use Hifiberry. After attaching the board to my pi, and enabling i2s in the browser (and rebooting), it wouldn’t recognise any audio hardware.
The solution, I found, was in /etc/modules, where this is the recommended setup at hifiberry.com:
snd_soc_bcm2708 snd_soc_bcm2708_i2s bcm2708_dmaengine snd_soc_pcm5102a snd_soc_hifiberry_dac
The final line differs in the Volumio distro for RPi (it is snd_soc_rpi_pcm5102a), but by appending snd_soc_hifiberry_dac, aplay -l would recognise the hifiberry.